1. Field of the Invention
This invention relates to a telescopic extension for a household appliance and a method for assembling thereof.
2. Related Art and Other Considerations
EP-B1-0 520 534 describes a telescopic extension for a vacuum cleaner, comprising an inner tube and an outer tube, sliding tightly one within the other, a sleeve, a constraining means between the inner and outer tube, a thrust slider and an actuating pushbutton.
The inner tube is provided with a row of notches of a preselected shape and the outer tube has a tubular end portion of a flared shape, which is integral with the outer tube and carries a sleeve fastened to its interior.
The constraining means consists of a small cylinder integral with a small plate provided with a pin. By means of the pin and the small plate, the small cylinder is rotatably supported in a hollow of the sleeve. The sleeve has an opening through which the small cylinder can engage a notch of the inner tube and disengage from the same.
In this telescopic extension, the thrust slider is integral and is formed as a single piece with the actuating pushbutton.
The thrust slider is slidingly supported inside the hollow of the sleeve and is subjected to the action of spring means.
The spring means operate the thrust slider to engage the small plate integral with the small cylinder and pin, so as to force the latter into the notch of the inner tube and to lock the inner tube in the outer tube. The extension thus assumes a preselected length.
For adjusting the extension""s length, the actuating pushbutton is manually pushed against the action of the spring means, so as to allow the thrust slider to disengage from the small plate and to let the small cylinder exit from the notch of the inner tube, thus unlocking the inner tube from the outer tube. By sliding the inner tube in the outer tube, the extension assumes the desired length.
For assembling the extension, the sleeve is fitted over the internal tube and the pushbutton-slider assembly is pre-mounted in the hollow of the sleeve, together with the spring means and the constraining means. The sleeve is then inserted in the tubular end portion, centered with respect to it, and the inner tube is mounted inside the outer tube. For allowing the pushbutton protruding from the slider to pass through, the tubular end portion of the outer tube must have an opening extending up to the outer rim and forms an inlet mouth for the slider-pushbutton assembly.
An opening of this shape and width has the disadvantage of weakening the outer tube and thus reducing its resistance to the working stresses.
Moreover, the need to hold the slider, the spring means and the constraining means firmly inside the hollow of the sleeve, before and while inserting the sleeve in the tubular end portion, make the assembling difficult and expensive.
EP-B1-0 601 620 describes a telescopic extension for a vacuum cleaner which comprises, as for the extension of EP-B1-0 520 534, an inner and an outer tube sliding tightly within each other, a sleeve, a constraining means between the outer and inner tube, a thrust slider and an actuating pushbutton.
In this second extension, the thrust slider is always integral and is formed as a single piece with the actuating pushbutton, while the sleeve is fastened to the outer tube. A tubular end portion, which is separate from the outer tube and has an internal diameter wider than the outer diameter of the outer tube, is fitted over the sleeve. The constraining means and the thrust slider are movably supported in a hollow of the sleeve.
The separate tubular portion has an opening extending up to the external rim and forms an inlet mouth for the slider-pushbutton assembly so as to allow the pushbutton protruding from the thrust slider to pass through. The outer tube also has an opening of the same shape, which allows the constraining means to engage a notch of the inner tube, and has a width capable of housing a projection of the sleeve, which allows it to be centered with respect to the outer tube.
This second extension is rather stronger than the first one, but its assembling is still quite difficult and expensive for the reasons already mentioned.
DE-A-42 00 526 discloses a telescopic extension for a vacuum cleaner comprising an inner tube, an outer tube, a sleeve arranged between them, a constraining small cylinder, a thrust element and an actuating knob.
The thrust element is formed by a flattened curved plastic piece comprising a quadratic body provided with a rectangular notch and a T-shaped projection. A groove for housing a torsion spring is arranged between said body and said projection.
The outer tube is provided with an opening having two narrow portions and two enlarged portions.
In turn, the actuating knob has four connecting small feet which are provided with undercuts directed towards the outside thus forming outer small teeth.
For assembling said extension, said constraining small cylinder, thrust element and spring are housed in said sleeve that is inserted in a flared portion of the outer tube. Then, when fastening the actuating knob to the thrust element, said thrust element is pressed against the action of the spring in direction of the arrow R of FIG. 5 in order to ring said thrust element under said opening of said outer tube in a position (outside the operating stroke) such that the respective T-shaped projection is located under the first enlarged portion of said opening and the respective notch is located under the second enlarged portion of said opening.
In said position, the two front connecting small feet of said actuating knob engage the T-shaped projection of said thrust element and the two near connecting small feet penetrate inside the notch of said thrust element.
Afterwards, upon releasing said thrust element, the spring pushes the actuating knob in the direction of the arrow L of FIG. 5 and brings the undercuts of the four small feet under the edges of the narrow portions of the opening of said outer tube. The actuating knob is so fastened to both the thrust element and the outer tube.
Said assembling method is very complex, time consuming and expensive.
Moreover, in the extension of DE-A-42 00 526, every time the actuating knob is driven to perform forward and rearward strokes for adjusting the length of the extension, the undercuts of the small feet slide with attrition along the edges of the narrow portions of the opening of said outer tube. Thus, said small feet undergo a quick earing whih causes clearance and even notching. This is a quick failure of said actuating knob.
A first object of this invention is a telescopic extension for a household appliance, preferably a vacuum cleaner, stronger and more efficient than those described in the foregoing documents.
A second and even more important object of the invention is to allow the structure of this telescopic extension to be manufactured and assembled in a simpler and more economical manner than that required by known extensions.
According to a first aspect, this invention relates to a telescopic extension for a household appliance comprising an inner tube and an outer tube (sliding tightly within each other), a sleeve, a constraining means capable of fastening the inner and outer tube, a thrust element in engagement with the constraining means under the action of spring means, and actuating means operatively connected to the thrust element. The inner tube is provided with a row of notches of preselected shape and a tubular end portion provided with a slot being associated with the outer tube. The sleeve is fastened to the tubular end portion. The constraining means, thrust element, and spring means are movably supported in the sleeve. The thrust element acts on the constraining means, under the action of the spring means, to force the constraining means into one notch to lock the inner tube in the outer tube. The actuating means is capable of disengaging the thrust element from the constraining means to let the constraining means exit from the notch and unlock the inner tube from the outer tube, thereby allowing the inner tube to slide in respect of the outer tube for adjusting the length of the extension. The actuating means is a separate piece from the thrust element and has protruding wings capable of penetrating the slot. The tubular end portion has a relief forming a niche. The sleeve is provided with a projection which is inserted in the niche and has a hollow wherein the constraining means, thrust element, and spring means are completely housed. The thrust element, in turn, is formed by a lengthened, flattened slider provided with a narrow portion having recesses. The protruding wings of the actuating means are provided with inner small teeth capable of being snap-on coupled with the recesses.
According to a second aspect, there is provided a method for assembling a telescopic extension for a household appliance, the appliance comprising an inner tube, an outer tube, a sleeve, a constraining means capable of fastening the inner tube and outer tube, a thrust element, actuating means, and spring means. The inner tube is provided with a row of notches having a preselected shape and a tubular end portion provided with a slot being associated with the outer tube. The actuating means is a separate piece from the thrust element and has protruding wings capable of penetrating the slot. The method comprises the following steps:
a) fitting the sleeve over one of the inner tube and outer tubes,
b) movably placing the constraining means, thrust element, and spring means in the sleeve,
c) inserting the inner tube in the outer tube so as to tightly slide one within the other and inserting the sleeve in the tubular end portion, and
d) inserting the wings of the actuating means in the slot of the tubular end portion, characterised in that
e) in step b), the constraining means, thrust element, and spring means are completely housed into a hollow of a projection of the sleeve,
f) in step c), the sleeve is centered in respect of the outer tube by means of the projection which fits a niche of a relief of the tubular end portion, and
g) in step d), inner small teeth of the wings are snap on coupled to recesses of a lengthened, flattened slider which forms the thrust element so that the actuating means are fastened to the thrust element.
The telescopic extension of this invention has the advantage of being very compact and capable of withstanding the working stresses.
The method of assembling according to this invention considerably simplifies the assembling steps and eliminates mounting difficulties and errors, because the thrust element and the spring means are completely housed in the hollow of the sleeve and remain properly positioned therein when the sleeve is inserted inside the tubular end portion. Thereafter, the actuating means are fastened to the thrust element by causing their coupling elements to penetrate the slot in the tubular end portion.
Thus, the method of this invention substantially reduces the assembling time and costs, and, moreover, it can be easily automatized.